Incomplete milking means that an unacceptable amount of milk is left in the udder after teatcups are removed.
Milk left in the alveoli is residual milk. Milk left in the ducts or udder cisterns is referred to as available milk or stripping’s.
Residual milk cannot be removed, even by careful machine or hand-stripping, without an injection of oxytocin. Typically, residual milk may be 1-3 kg or about 10-20% of total milk in the udder. Higher amounts may result from incomplete milk ejection associated with poor milking routines, frightened or nervous cows, sore teats or uncomfortable milking equipment.
Lactating heifers have less residual milk than older cows. The percentage of residual milk is greater for lower producing cows than for higher producing cows. Cows with a higher percentage of residual milk usually have a lower persistency of lactation
Incomplete removal of the available or stripping’s milk occurs when:
• Teatcups are removed well before the last of the available milk drains into the udder cisterns,
• The milk pathway between the udder cistern and teat sinus, in one or more of the four quarters, becomes blocked near the end of milking. Such blockages occur when clusters do not hang evenly on the udder and/or when one or more of the four teats moves too deeply into its teatcup—referred to as teatcup crawling. The most common causes of incomplete milking due to such flow restrictions near the end of milking
• Poor condition of the liner;
• Clusters that do not hang evenly on the udder because the connecting hoses are too long, too short, twisted or poorly aligned in relation to the cow;
• High milking vacuum levels;
• A mismatch between the claw inlet and the short milk tube causing partial closure of the short milk tube where it joins the claw.
Evidence between completeness of milking and new mastitis infection rates is contradictory. Most of the older research suggested that mastitis increased when the last drop of milk was not removed.
Latest studies showed that small quantities of milk left in the udder did not increase new infection rate or clinical mastitis, and some studies found higher levels of infection associated with machine stripping.
The latest findings are not unexpected. It is likely that the new mastitis infection rate would be increased by excessive machine stripping which causes sudden air admission into one or more teatcups just before the teatcups are removed.
Most liner slip is before and after milk let down. Any increase in rate of cup slippage can increase the risk of mastitis.
Monitoring milking, the mean stripping’s yield is typically less than 0.25 kg per cow. A problem exists if an average of more than 0.75 kg of stripping’s milk is left in a cow’s udder when teacups are removed.
Uneven weight distribution between the four quarters can cause incomplete milking, uneven milk-out and liner slips. Ideally, the milking unit should hang squarely
Twisting or pulling of the milk hose can alter the alignment.
There is a long-held belief that leaving milk in the udder will lead to mastitis.
The greater concern is the risk of over-milking, which occurs when attempting to extract every last drop of milk from the udder. This can lead to teat-end damage.
Over-milking may also Increase the likelihood of transfer of infection between quarters during the period of little or no milk flow. Consequently, over milking should be avoided.
A moderate level of incomplete milking (e.g. strip yields of up to 1 litre of milk per udder) does not increase the risk of mastitis.
Leaving the unit on with no milk flow can elevate intramammary pressure resulting from milk retained in the udder after milking cessation this then could lead to tissue damage and pain.